Method for supplying foodstuff samples for microbiological testing

ABSTRACT

Methods for supplying a foodstuff sample for microbiological testing comprise supplying the sample in a plastic bag, adding physiological nutrient solution to the sample in a specified weight ratio, mechanically comminuting and homogenizing the contents of the bag, and removing a partial quantity of the contents of the bag by means of pipette via a filter as sample liquid. The methods further comprise injecting the same liquid onto at least one nutrient medium situated in a petri dish and inserting the injected petri dish into an incubator. In the communution and homogenization of the contents of the bag, the bag is clamped shut and pressed between a fixed jaw and two jaws which oscillate alternately. In the injection of the nutrient medium, the sample liquid is injected in a spiral shape onto the nutrient medium. Additionally, a laboratory robot system is employed.

The invention relates to a method for supplying foodstuff samples forthe microbiological testing.

To date, microbiological examinations were carried out exclusively byhand. This is justifiable, when few samples are concerned. However, inthe foodstuffs industry, samples have to be examined frequently and inlarge numbers with regard to the bacillus factor. A further complicationis that in microbiological examinations, work must be carried out understerile conditions, and too great a time must not elapse from thedelivery of the samples up to installation in the incubator, becauseotherwise owing to the multiplication of the bacilli even at roomtemperature, the result of the examination would be falsified.

The invention is based on the problem of developing the testing methodof the type indicated in the introduction such that it can runautomatically after preparation of the samples up to installation of theinjected nutrient media into the incubator.

This problem is solved according to the invention.

An essential feature of the method according to the invention is the useof a laboratory robot system with a handling robot and a programmablecontrol unit. Such a system is indeed already known as a universalsystem to carry out various laboratory operations (laboratory robotsystem of the firm Zymark Corporation, Hopkinton, MA USA). However, thishas never until now been installed and used to carry out the relativelycomplex microbiological examinations. The result which is aimed foraccording to the invention is only achieved in that the laboratory robotsystem is used in combination with two further quite specific items oflaboratory apparatus which are likewise already known per se, namely theso-called stomacher and the so-called spiral-plater. The stomacherallows the comminution and homogenization of samples, which arecontained in plastic bags, with the plastic bag closed. Through this itbecomes possible to leave the samples, which are to be examined, inplastic bags during the entire examination. This, in turn, is aprerequisite for the fact that the samples can be handled individuallyby the laboratory robot, without the samples or residues of sampleshereby coming into contact with each other, whereby the result of theexamination would be falsified. The microbiological examination furtherrequires that sample liquid with differing concentration is injected outfrom each sample onto the nutrient medium. The spiral-plater, with whichthe sample liquid is injected onto the rotating nutrient medium througha nozzle which is moved in radial direction, i.e. in a spiral shape andhence in one working step in differing concentration, creates theprerequisite for the fact that this process can also be handled by thelaboratory robot system, which would scarcely be possible with amultiple-stage injecting out, e.g. with sample liquids of differentconcentrations, owing to the too high complexity of such a process andowing to too great an expenditure of time. In all, it is achieved by themethod according to the invention that in particular samples offoodstuffs can be examined fully automatically in large numbers. It ismerely necessary to place the samples, which have been removed forexample in the foodstuffs factory, in the plastic bag in readiness. Theyare then treated fully automatically, according to the method of theinvention, up to installation of the ready injected nutrient media, inpetri dishes, into the incubator.

In one embodiment of the new method according to the invention, theaccurate dosing of the samples, hitherto performed, which would only beable to be carried out by the robot with difficulty, is not necessary.The samples which have only been estimated approximately as regardstheir weight, can be treated just as they arrive after removal. Thedesired precise weight ratio between the sample and the physiologicalnutrient solution is produced through corresponding dosing of thenutrient solution, which is preferably able to be carried out easilyautomatically as a time-dependent, but also volumetric dosing. Here, thecontrol unit takes charge of the evaluation of the weighing of thesample and the calculation of the necessary quantity of nutrientsolution.

The another embodiment, the new method makes possible the furtheracceleration thereof through the "nesting" of sections of the process,whereby the stomacher is very soon freed for a new sample. In addition,the clean removal of the plastic bags of which the contents have beenevaluated, is ensured by simply dropping into the waste opening.

A further embodiment acts in the same direction. The mechanical screensurrounding the pipette acts as a filter, through which only sampleliquid can pass. Of course, the pipette must be cleaned and carefullysterilised after each removal process. Through the activation of thedisinfection and cleaning bath by ultrasonics, at the same time amechanical cleaning in particular of the screen of the pipette isachieved, whereby one is saved from exchanging a filter after eachremoval process. To save time, the suction pipette can be allowed todrain, whilst the stomacher is in operation.

The spiral-plater, known per se, has a built-in dosing pump. In theconventional use within examinations which are carried out by hand, thesample liquid which is to be injected out is sucked in by means of thebackwardly-running dosing pump through the injection nozzle of thespiral-plater. Normally, two nutrient media are injected in a spiralshape with the sample liquid from one sample. Until now, this meant twosuction processes. In one embodiment of the new method, sample liquidfor the spiral-plater is only sucked in once, and the injection ofseveral nutrient media is nevertheless possible, which further complieswith the automatic carrying out of the method.

The method may include a step for the reliable mutual separation of thesamples. It is likewise carried out automatically, controlled by thecontrol unit.

An essential prerequisite for the automatic running of the examinationis a reliable handling of the filled plastic bags by the laboratoryrobot. This is ensured particularly well when the laboratory robot forthe handling of the plastic bags uses a hand in. On transportation, theplastic bag is clamped between the clamping jaws. To open the bag, theopenings in the clamping jaws are acted upon with negative pressure andthe clamping jaws are moved apart. The openings can also remain actedupon with negative pressure with the clamping jaws in closed state. Thenthe plastic bags are secured particularly reliably.

In the course of an examination, each plastic bag has to be transportedseveral times and in so doing has to be deposited so as to be accuratelypositioned at its destination, e.g. on the scales or in the stomacher orin the holding device. In order that this is successful with accuracy,unimpaired by inherent movements of the bag, the manner of procedureaccording to claim 10 has proved to be advantageous. Through the openingof the plastic bag during the intermediate stop, the plastic bag isstabilised and oscillation movements of the bag cease.

Usually in microbiological examinations, specific nutrient media areadditionally injected with the sample liquid, but only in a fixedconcentration. To save nutrient media, it is usual to inject eachnutrient medium several times with different samples--of course atdifferent sites, e.g. sectors thereof. This injection can advantageouslytake place within the framework of the method according to theinvention.

The petri dishes with fresh nutrient medium, and namely both those forthe spiral injection and also those for the multiple injection, areexpediently kept ready for automatic handling. In so doing, thelaboratory robot always finds the individual petri dish at the samelocation, which is important for an automatic running of the processwhich is as simple as possible. Accommodation in a stack, moreover,saves space. In addition, the stack magazines can be replenished duringthe running of the examination, without disturbance thereof.

As operations must be carried out at all locations under scrupulouslysterile conditions, the petri dishes are closed with lids in theconventional manner. It has proved to be difficult to also leave theremoval and replacement of the lids to the laboratory robot itself.

The invention with further advantageous details is explained below bymeans of an example embodiment which is represented diagrammatically.The single figure shows in diagrammatic plan view a laboratoryarrangement for the automatic microbiological examination of samples offoodstuffs.

The entire examination arrangement, represented in the single figure, issituated on a large table plate and comprises several individual itemsof apparatus. In the centre of the arrangement is a laboratory robot 1.This comprises a horizontal arm 2, which stands away from a verticalcolumn 3. The arm is adjustable as regards its height on the column 3and through rotation of the column 3 about its vertical central axis inhorizontal direction is able to be oriented in both directions over acircular arc of somewhat more than 360°. In addition, the arm 2 can bedisplaced with respect to the column 3 in its longitudinal direction, sothat its free end assumes differing distances from the column 3. Thefigure shows the arm 2 in a partially extended position. At the freeend, the arm 2 has a drive unit 4, with which different robot hands,which are movable in each case in several degrees of freedom, are ableto be coupled through an insertion process. In the method according tothe invention, operations are carried out with two different robot hands5 and 6, which are to be explained in further detail.

The laboratory robot 1 belongs to a laboratory robot system whichadditionally comprises a control unit 7, based on a microprocessor, witha keyboard and a screen (not shown in further detail). The control unitis able to be programmed by the user, and controls the laboratory robot1 and all further items of laboratory apparatus taking part in theexamination, in accordance with the programme.

The items of laboratory apparatus taking part in the examination arearranged in a circle around the laboratory robot, so that they can bereached by the robot hand. Amongst the items of laboratory apparatus isa hole magazine 10 with a plurality of vertical holes arranged in arectangular grid, which holes are in each case equipped with adisposable suction pipette before commencement of an examination series.The disposable suction pipettes can be removed individually out of thehole magazine 10 by the robot 1 by means of the hand 6. The control unit7 is able to be programmed by means of a sub-programme such that itnotes the hole out of which a suction pipette was respectively lasttaken, and guides the robot hand to the next respective, still filled,hole on the following removal.

Three similar stack magazines 11, 12 and 13 follow the hole magazine 10in clockwise direction, which stack magazines are to hold petri dishes,in which there are nutrient media. Each stack magazine contains thepetri dishes, which are closed by lids, in two stacks. Associated witheach stack at the lower end there is a slider. e.g. 11a, which onactuation, controlled by the control unit 7, advances the respectivelylowermost petri dish of the stack into the range of action of therobot 1. The magazines 11 and 12 contain petri dishes, the nutrientmedium of which is divided into four sectors by cross-pieces in the baseof the petri dishes. They are intended for the so-called drop-plating,in which each sector of the nutrient medium is injected with a drop ofsample liquid from a different sample in each case. The magazine 13contains normal petri dishes without cross-pieces, and a correspondinglycontinuous nutrient medium, which is intended for the so-calledspiral-plating, in which sample liquid is injected out in a spiral shapeonto the nutrient medium.

Between and in front of the two stack magazines 11 and 12, there is anopen container 14 with a disinfection and cleaning bath, which isactivated by ultrasonics. Adjacent to the container 14, a drip support15 is arranged, which is to be explained in further detail.

Following the stack magazine 13 in circumferential direction is aso-called stomacher 16. This is an apparatus known per se for thecomminution and homogenization of samples, which are situated in plasticbags. At the left-hand end, the stomacher 16 has a shaft 17 which isable to be closed by a flap. The plastic bags are inserted from aboveinto the opened shaft, where, after the automatic closure of the shaftflap, brought about by means of a motor or a hydraulic cylinder, theyare pressed between a fixed jaw and two jaws which lie adjacent to eachother and which are moved alternately back and forth.

In front of the stomacher 16 there is an electronic scales 18. Followingthe stomacher 16 in circumferential direction is a mounting, notrepresented in further detail, for one hand 5 of the robot. The hand 5is intended for the handling of plastic bags filled with samples. Forthis, it has two clamping jaws 8, between which the upwardly openplastic bags can be grasped and clamped at their upper rim. In theclamping jaws 8, openings are provided which are able to be acted uponby negative pressure in a manner not shown in further detail. When theseopenings are acted upon by negative pressure, the walls of the bagsremain adhered to the respective jaw, so that the bags can be opened bymoving the clamping jaws 8 apart, and nevertheless do not drop out ofthe clamping jaw.

Between the mounting for the hand 5 and the robot 1, there is a fixedholding station 19 for the plastic bags, which in an analogus manner tohand 5 has two clamping jaws 20 respectively with negative pressureopenings. Under the mounting 19 there is a waste opening 21 in the tableplate. In radial direction immediately adjacent to the stationaryholding station 19 at the edge of the waste opening 21 a stripper 22 isfixedly mounted.

Following the mounting for the hand 5 in circumferential direction arethree similar bag magazines 23,24 and 25, in each case radially aligned.Three bag magazines are shown merely by way of example. In practice, inparticular, more may also be present. In the arrangement to be found inpractical testing, finally five bag magazines were provided. Each bagmagazine has several upwardly open openings, elongated in radialdirection, into which plastic bags filled with samples of foodstuffs canbe inserted. In circumferential direction, the elongated openings have adistance from each other such that the plastic bags can be graspedindividually by means of the hand 5 or respectively its clamping jaws 8at the upper rim, and can be lifted out of the magazine. As in the caseof the hole magazine 10, a sub-programme makes provision for the controlunit 7 to guide the robot 1 or respectively its hand in succession tothe next respective magazine opening.

Adjoining the three bag magazines in circumferential direction is aso-called spiral-plater 26. This is an item of apparatus known per se,with a rotatable receiving plate 27 for petri dishes. Over the receivingplate 27, in a manner not shown here in further detail, there is aninjection nozzle, which is movable with respect to the receiving plate27 in radial direction, from which nozzle sample liquid is sprayed,which is to be injected out by means of a dosing pump. Throughsimultaneous rotation of the receiving plate 27 and radial movement ofthe injection nozzle, the sample liquid is injected in a spiral pathonto the nutrient medium in the petri dish, and namely with acontinuously changing injection concentration, which depends upon therespective relative speed between the nozzle and the nutrient medium andalso, if applicable, on a corresponding control profile of the dosingpump. The spiral-plater has, in addition, a fixed intermediate depositsite 28 for the petri dish, at which its lid can be removed by means ofa suction- and lifting device which is not shown in further detail.Outside the spiral-plater 26 there is a control set 29 which, like allthe other items of laboratory apparatus, is connected to the controlunit 7. Via corresponding hose connections and hydraulic valves, thisbrings about on the one hand the "charging" of the spiral-plater withsample liquid, which for this purpose is sucked in through a screenpipette, which is to be explained in further detail, and on the otherhand brings about the flushing of the spiral-plater and of the screenpipette with water and disinfection liquid after each completedinjection process.

In circumferential direction adjacent to the spiral-plater a largeincubator 30 with a door 31 is set up, into which the petri dishes areinserted after injection of the nutrient medium by the robot 1, in, forexample, six stacks, whereby the control unit 7 by means of asubprogramme, in turn in an analogous manner to the removal from thehole magazine 10, notes the position of the respective uppermost petridish in the stack.

Finally, adjacent to the incubator, a mounting is provided for thesecond hand 6 of the robot 1. This is a universal hand with grippers,which are suited to the handling of the petri dishes and the disposablepipettes. Controlled by the control unit 7, the robot can couple the twohands 5 and 6 selectively with the mounting 4, whereby the respectiveunused hand remains deposited on the mounting associated therewith,until it is required again.

To carry out a microbiological examination series, for example in afoodstuffs factory, samples of foodstuffs are removed, which have onlybeen roughly estimated as regards their weight, and are filled into theplastic bags. The plastic bags filled with the samples are inserted byhand into the corresponding openings of the bag magazines 23 to 25. Eachmagazine has, for example, eight openings, so that with, for example,five magazines, up to forty plastic bags can be inserted. In addition,the stack magazines 11,12 and 13 are filled with petri dishes, in whichthe nutrient media required for the examination are to be found.Controlled by the correspondingly programmed control unit 7, the samplesare now processed fully automatically in succession, and namely in thefollowing sequence of operations:

The robot 1 takes up the hand 5 and moves it to the first plastic bag inthe magazine 23. This is grasped between the clamping jaws 8, is liftedout of the magazine, transported to the scales 18 and deposited on itsweighing dish by opening the clamping jaws 8. On opening of the clampingjaws, the hand is also moved in vertical direction, in order to ensurethat the plastic bag does not remain hanging on the clamping jawsinadvertently. The control unit 7 interrogates as to the weight of thefilled plastic bag and determines from this the weight of the samplethrough subtraction of the known weight of the bag. The bag is nowgrasped by the hand 8 again, is brought beneath an outlet connection 32for nutrient solution, provided adjacent to the scales 18 and is openedthere. The bag is now filled with nutrient solution. Here, a specifiedquantity of nutrient solution, corresponding to the determined sampleweight, is dosed by the control unit 7, so that the sample and thenutrient solution are in a desired weight ratio. A time-controlled pumpis used for dosing.

Then the bag is closed again and is inserted into the opened shaft 17 ofthe stomacher 16. The bag still remains held by the hand 5, whilst theshaft 17 is closed by motor by means of the shaft flap. At the end ofthe closure movement, the shaft plate firmly clamps the bag. The hand 5moves away and the stomacher begins to operate in the manner explained.

In the disinfection- and cleaning bath in the container 14, the screenpipette already mentioned, i.e. a pipette surrounded by a finemechanical screen, is deposited, which is connected via a hose to thecontrol set 29. The robot 1 travels to the screen pipette, lifts it outof the bath and deposits it on the drip support 15, where the adheringdisinfection solution can drip off. Then it returns to the stomacher,grasps the plastic bag there, in the shaft 17 which has opened again inthe meantime, and carries the plastic bag over into the stationaryholding station 19. On the way there, the robot 1 takes an intermediatestop, at which the plastic bag is opened and is thereby brought to rest,which facilitates the subsequent accurate positioning between theclamping jaws 20 of the stationary holding station 19. After the robothand 5 has moved away, the plastic bag is now opened in the holdingstation 19 through moving the clamping jaws 20 apart. In the meantime,the robot fetches the screen pipette from the drip support 15 andcarries it, after brief immersion into a washing bath, not shown, intothe opened plastic bag. Via the control set 29, a certain quantity ofthe sample liquid contained in the plastic bag is now sucked into a hosesection in the control set 29, keeping back the solid components of thesample. Then the screen pipette is withdrawn again out of the plasticbag and is transported back into the disinfection- and cleaning bath inthe container 14. Then the robot 1 exchanges the hand 5 for the hand 6.With the hand 6 it removes a disposable pipette from the hole magazine10 and then--whilst holding the disposable pipette secure--removes apetri dish from the stack magazine 13. It carries this petri dish to theintermediate deposit site 28 of the spiral plater 26, where the lid ofthe petri dish is removed, and from there onto the receiving plate 27.There, the nutrient medium of the petri dish is injected, for which thesample liquid contained in the hose section is pressed with hydraulicpressure into the dosing pump of the spiral-plater and is sprayed out bymeans of the dosing pump through the injection nozzle in the describedmanner. Whilst the injection process is running, the robot 1 immersesthe disposable pipette into the opened plastic bag in the holdingstation 19 and sucks up further sample liquid therewith. Then the robotmoves back to the spiral-plater, grasps the petri dish there, carries itto the intermediate deposit site 28, where the lid is put on again, andbrings it from there into the incubator 30 onto one of the three stackswhereby the whole time the filled disposable pipette travels with it.Then a second petri dish is removed from stack magazine 13, istransported to the spiral-plater in the described manner, is openedthere and is placed onto the receiving dish 27.

Whilst the second petri dish is injected, the robot moves to one of thetwo stack magazines 11 or 12. There, by means of a fixed lifting andsuction device, the lids of two petri dishes are removed and in eachcase a new sector of their nutrient medium is injected dropwise out ofthe disposable pipette. Then the lids are put on again. Then the robottravels with the hand 6 to the stripper 22, by means of which thedisposable pipette is stripped off by raising the hand, so that it fallsinto the waste opening 21. Then the second petri dish, which has beeninjected in the meantime, is brought from the spiral-plater 26 to theincubator 30. Finally, the plastic bag is freed from the clamping jaws20 of the holding station 19 and likewise falls into the waste opening21. The hand 6 is exchanged again for the hand 5 and a new operatingcycle can begin. Through a back and forth movement of the sliders of themagazine 13, two new petri dishes are brought into the range of actionof the robot 1. When at the end of a cycle all four sectors of the petridishes from the magazines 11 and 12 are injected, before a changeover ofhands, in an interposed operating step the corresponding petri dishesare also transferred into the incubator 30 and new petri dishes arebrought into the range of action of the robot 1 by back and forthmovement of the sliders of the magazines 11 and 12.

In an alternative to the operating sequence which has been explained,the plastic bags initially remain in the stomacher after the comminutionand homogenisation of the sample, so that the sample liquid is removedthere from the opened bag. At the end, the plastic bag is throwndirectly into the waste opening 21. Through this, the operating sequenceis somewhat simpler. On the other hand, the risk of an undesiredcontamination of the stomacher is somewhat greater.

We claim:
 1. Method for supplying a foodstuff sample for microbiologicaltesting, comprising supplying the sample in a plastic bag, addingphysiological nutrient solution to the sample in the plastic bag in aspecified weight ratio, mechanically comminuting and homogenizing thecontents of the bag, removing a partial quantity of the contents of thebag by means of a pipette via a filter as sample liquid, injecting thesample liquid onto at least one nutrient medium situated in a petridish, and inserting the injected petri dish into an incubator; saidmethod further comprising, in the comminution and homogenization of thecontents of the bag, clamping the plastic bag shut and pressing theplastic bag between a fixed jaw and two jaws which oscillatealternately; in the injection of the nutrient medium, injecting thesample liquid out in a spiral shape onto the nutrient medium; employinga laboratory robot system including a laboratory robot to carry out allhandling processes by means of a mechanical hand; and controlling therobot and all participating laboratory apparatus with a control unitprogrammed according to a sequence of examination.
 2. Method accordingto claim 1, wherein the sample in the plastic bag is weighed and thephysiological nutrient solution is added respectively in a quantitycorresponding to the weight which was determined.
 3. Method according toclaim 1, wherein the processed plastic bag is transported out of astomacher where its contents are comminuted and homogenized to astationary holding device where the sample liquid is removed.
 4. Methodaccording to claim 3, wherein the stationary holding device is situatedover a waste opening.
 5. Method according to claim 3, wherein a pipetteis used for the removal of sample liquid, which pipette is surrounded bya mechanical screen, and wherein after each removal operation thepipette is inserted into a disinfection and cleaning bath activated byultrasonics.
 6. Method according to claim 5, wherein the pipette isremoved from the disinfection and cleaning bath and is set aside to dripwhile the stomacher is in operation.
 7. Method according to claim 1,wherein the sample liquid is sucked out of the plastic bag into a hosesection and is transported therefrom through hydraulic pressure into adosing pump included in a spiral plater employed for injecting thesample liquid in the spiral shape.
 8. Method according to claim 7,wherein in each case after the injecting of the sample liquid, thespiral-plater is flushed with cleaning and disinfection liquids. 9.Method according to claim 1, wherein for the handling of the plasticbags, the laboratory robot uses a hand with two clamping jaws in whichopenings are provided, which openings are activated by negative pressureto open the plastic bags.
 10. Method according to claim 9, wherein anintermediate stop is made during transportation of the plastic bags tosteady the movement of the bags, and during the intermediate stop, theplastic bag is opened.
 11. Method according to claim 1, whereinadditional sample liquid is removed from the plastic bag by means of adisposable suction pipette, and the additional sample liquid is injectedout onto at least one nutrient medium in a petri dish, which mediumreceives injections of several samples.
 12. Method according to claim11, wherein the disposable suction pipette is removed in each case bythe laboratory robot from a hole magazine and, after injecting theadditional sample liquid, is stripped from the robot hand over a wasteopening.
 13. Method according to claim 1, wherein petri dishes withfresh nutrient medium are kept in stack magazines from which the dishesare individually advanced by means of a slider into the range of actionof the laboratory robot.
 14. Method according to claim 13, wherein thepetri dishes are closed by lids, which lids are removed by means ofsuction lifters on a spiral-plater employed for injecting the sampleliquid in the spiral shape and/or on the stack magazines, and which lidsare subsequently placed in position.